A heating, ventilation, and air conditioning (HVAC) subsystem of a vehicle typically includes a compressor, a condenser, an expansion valve, an evaporator, a heater core, a blower, and a flapper valve. The compressor pressurizes refrigerant flowing from the evaporator to the condenser, and thereby circulates the refrigerant through the HVAC system. The condenser cools refrigerant as the refrigerant flows through coils in the condenser. The expansion valve reduces the pressure of refrigerant flowing from the condenser to the evaporator.
The blower forces air through the evaporator, and the heater core, into the interior of the vehicle. Refrigerant flowing through coils in the evaporator absorbs heat from air flowing across coils in the evaporator, thereby cooling the air. Engine coolant flowing through the heater core rejects heat to air flowing through the heater core, thereby heating the air.
The position of the flapper valve controls the amount of airflow through the heater core in order to achieve a desired air temperature within a cabin of the vehicle. In one example, the position of the flapper valve is adjusted to direct all of the airflow through the heater core when maximum heating is desired. In another example, the position of the flapper valve is adjusted to prevent any airflow through the heater core when maximum cooling is desired.
When an engine is automatically stopped (i.e., Autostop eng Off-engine turned off independent of an ignition system of the vehicle), the ability of the HVAC system to cool the vehicle cabin diminishes substantially which may result in periods of discomfort to passengers in warm conditions. Thus, it is desirable to means of controlling the HVAC system to maintain comfort for passengers during an autostop condition while increasing system efficiency and performance.